1. Field of the Invention
This application relates to fixation devices. More particularly, it relates to bone fixation devices made from bone tissue, bone powder, and related natural material.
2. The Prior Art
In repairing bone fractures or breaks and in other bone repair, it is customary to use pins, nails or screws to hold the bone together to allow regrowth and healing. Such screws, pins and other fixation devices are customarily constructed of metal, e.g. surgical stainless steel, or polymeric materials. Resorbable polymers have found wide use in recent years. Polyglycolide, polydioxanone and polylactide polymers, polymers that are also used in absorbable suture materials, have been successfully used. Such fixation devices come in various shapes and sizes, each designed to provide some special benefit. For example, U.S. Pat. No. 5,417,533 provides a bone screw having a helical thread that gradually increases in thickness from the tip to the head of the screw. This screw design is said to increase the screw's resistance to tearing out of the bone and have the further advantage of being inserted with minimum tearing or cracking of the bone.
AO/ASIF or Arbeitgemeinschaft fur Osteosynthesisfragen (English translation, Association for the study of Internal Fixation[ASIF]) screw designs are commonly and widely used. Screw fixation devices are generally inserted into pre-drilled and tapped holes in the bone or cartilage to be repaired. Pins are used where appropriate. Pins are, of course, distinguished from screws by the lack of threads and leads and are more commonly used to provide rigidity to bone rather than compression. Fixation plates are used to hold bone or other skeletal parts into place. The plates are usually held in place by screws. Anchors are also used which provide an attachment for sutures in the body.
Metal fixation devices and absorbable polymer devices are not without problems. Metal pins and screws often need to be removed, causing additional trauma to the patient and causing weakening of the repaired bone. One advantage of the polymer devices is elimination of the need to remove the device when the bone has healed. However, the long-term consequences of polymer absorption are not known. Moreover, absorbable polymers can cause irritation and sterile abscess from the decomposition products of the polymer.
Bone grafting is also well known. Grafting is the process in which live or nonliving bone is placed between or into living bone in the body. The graft becomes incorporated into the renewed bone structure of the living bone as it replaces itself and regrows. New bone growth replaces the graft and eliminates the graft material over time whether the graft is of nonliving or live bone tissue. Freeze dried sterile bone is most often used. When cortical bone is used in grafts the absorption of the graft material takes a long time, usually months. For cancellous bone grafts the absorption is often effected in days or weeks. Heretofore, bone fixation and bone grafting have been separate operation. Fixation is the holding of bone in place for healing and grafting is the provision of a bone structure for regrowth of new bone.
I have now discovered that the disadvantages of the present steel and/or polymer fixation devices can be obviated by use of fixation devices made from bone tissue. Moreover, the fixation device is, in effect, grafted into the bone in which it is used and does not require subsequent removal. For human use, human bone tissue is used. For veterinary use, appropriate animal bone or human bone tissue is used. Human bone tissue is readily available from a number of "Bone Banks". These bone banks provide suitable bone tissue that has been cleaned and sterilized for human therapeutic use, such as in bone grafts and the like.